Manufactured parts are often fabricated using a variety of mechanical and thermal processing steps, such as heat treating, welding, and others, that cause mechanical stress within the materials. Residual stress remaining in a manufactured part has been found to adversely affect fatigue life, corrosion susceptibility, and strength, wherein areas near weld joints have been found to be particularly susceptible to stress problems. In many machines and structures, component parts may suffer early degradation in load bearing capability, corrosion resistance, and/or catastrophic failure due at least in part to internal stress remaining after fabrication or welding. Furthermore, the repair and/or replacement of components is costly in many situations.
Localized internal stresses may cause accelerated failures due to stress corrosion, fatigue, and premature overload fractures. These failures can occur in bridges, aircraft structures, ship hulls, pipelines, liquid storage tanks, rails, and reactor vessels, as well as in many other structures. Relieving or reducing internal stress in large structures is sometimes difficult, particularly where the structure is in a remote location. For example, stress may occur as a result of welding pipes together in remote areas to create an oil pipeline, or from welding, forming, and/or assembling structural components in bridges, ships, or airplanes. For large and small structures, premature degradation or failure of the structure may result from remaining internal stresses. Durability and performance of welded parts are affected by internal stresses that can reduce fatigue life and corrosion resistance. Welding involves providing high temperatures to melt a welding rod or other filler metal used to join two sections of plates. The base metal joining surfaces are also heated to melting temperatures during the welding process. The presence of thermal gradients adjacent to the weld line affects the microstructure of the plate. Thermal gradients are the primary cause of residual stresses along the weld lines and contribute to diminished mechanical properties and reduced corrosion resistance in the heat-affected zone compared to the base material. In addition, welding, especially when coupled with variations in thickness, leaves significant internal stresses as the material attempts to adjust to the varying thermal gradients.
Accordingly, techniques have been developed for relieving internal stresses in manufactured parts that may be employed during or after fabrication or welding operations. However, conventional stress-relief processes are typically time-intensive, requiring application of energy to the stressed parts for long periods of time. In a manufacturing setting, lengthy stress-relief processes are costly in terms of total fabrication time, throughput, and energy. Time and energy are also an important consideration in stress-relieving structures in the field. For example, performing a stress-relief operation on an aircraft in a commercial airline fleet requires that the aircraft be grounded during the stress-relief operation. For large structures, such as welded pipes in a remote pipeline, ship or aircraft hulls, etc., the energy for the stress-relief operation often needs to be brought to the worksite, wherein time-intensive conventional stress-relief techniques are particularly costly. Accordingly, there remains a need for improved stress-relief techniques and systems for reducing stress in manufactured parts and/or welded structures.